1. Field of the Invention
The present invention relates to a fuel supply system which includes a fuel delivery valve for an internal combustion engine.
2. Description of the Related Art
Generally, fuel vapor generated in the fuel delivery valve at high temperature is discharged from the fuel delivery pipe through a pressure regulator and a return pipe to a fuel tank. In a device disclosed in Utility Model Unexamined Publication Sho 62-137379, a fuel pipe is connected between an upper portion of the delivery pipe and a pressure regulator to discharge the vapor to the fuel tank without storing in the delivery pipe.
In addition, many devices and systems are proposed to prevent emission of the fuel vapor from the fuel tank which is caused by fuel vapor generated in the delivery pipe and carried to the fuel tank. In other devices only a fuel pipe is connected to the fuel delivery pipe and a fuel-return-pipe is omitted, thereby reducing number of parts and the production cost. If the fuel-return-pipe is omitted, the inside of the delivery pipe is sealed except that it connects through injectors and the fuel pipe.
The conventional devices as described above have the following drawbacks.
First, if the return pipe is omitted from the above structure, the vapor in the delivery pipe has no way to go out and may accumulate in the delivery pipe, decreasing fuel injected into the engine and stopping the engine.
In order to obviate the above-mentioned trouble, U.S. Pat. No. 5,359,976 issued to the assignee of this application proposes a device in which the fuel pipe is disposed above the delivery pipe and connected by a branch pipe to an upper portion of the delivery pipe. All connectors of the injectors extend to locate the inlets of the injectors at upper portions of the delivery pipe so that the fuel vapor is mainly discharged through the branch pipe and the rest of the fuel vapor may discharge from the injectors without storing the vapor in the delivery pipe. However, the above device becomes complicated and large in size.
In order to improve the above device, Japanese Utility Model Unexamined publication Sho 63-196471 discloses a device in which a pressure regulator increases its valve opening pressure when the engine stops. Japanese Utility Model Unexamined Publication Sho 58-44477 discloses a device which has an inlet-passage-cut-valve to maintain the inside pressure of the delivery pipe high, thereby preventing generation of the fuel vapor.
However, these structures are required to have high-pressure-resistive members from the upstream portion of the fuel pump to delivery pipe, resulting in complicated structures.
The above two publications only disclose devices which have the return pipes.
Second, if the fuel-return-pipe is omitted from the conventional devices, pressure waves caused by operation of the injectors are transmitted to the fuel pipe and others from the delivery pipe, thereby causing harsh noise.